Embodiments of this invention relate to low noise amplifiers having noise cancellation and are suited for, but not limited to, implementation as semiconductor devices for amplification of signals at millimeter wave frequencies and ultra wideband CMOS applications.
Cancellation techniques have been employed especially in low-frequency electronic devices in order to minimize the presence of an undesired signal. For example, a replica of an undesired signal that is 180° out of phase with the undesired signal can be combined or added to the undesired signal in an effort to minimize the magnitude of the undesired signal. Under a “perfect” condition in which the replica signal is exactly 180° out of phase and has an equal magnitude to the undesired signal, adding these signals together will result in substantially total cancellation.
Cancellation of an unwanted signal using the above explained technique becomes much more difficult at higher microwave frequencies and well into millimeter wave frequencies. It becomes increasingly more difficult to generate the “perfect” replica signal at higher frequencies due to challenges in maintaining the perfect 180° out of phase relationship as well as an equal magnitude to the signal to be canceled. Even more challenges are present when the signal to be canceled is associated with an amplifier, especially where the amplifier operates over a substantial range of high frequencies.